The present invention relates to a viscous fluid type heater that generates heat by shearing viscous fluid in a heating chamber with a rotor and transmits the generated heat to heat exchange fluid in a heat exchange chamber.
The present assignee has proposed various types of engine-driven viscous fluid type heaters that function as auxiliary heat sources for vehicles. Such heaters typically include a housing, a heating chamber and a water jacket (a heat exchange chamber), which are defined in the housing. The heaters also include a disk-shaped rotor coupled to and driven by an engine with a drive shaft. When rotated, the rotor shears viscous fluid (for example, silicone oil having a high viscosity) thereby generating heat based on fluid friction. The heater uses the generated heat to heat circulating fluid (engine coolant) in the water jacket.
The disk-shaped rotor causes the relative speed between the disk and the fluid to be higher in the peripheral portion of the rotor. In other words, the fluid is sheared by a faster moving disk surface in the peripheral portion of the rotor compared to the fluid at the center portion of the disk. This causes the temperature of the viscous fluid at the rotor periphery to be higher than that of the fluid near the rotor center. If viscous fluid is heated to exceed its maximum heat resistance, the fluid quickly deteriorates. Deteriorated fluid fails to generate heat when sheared. Thus, localized deterioration of viscous fluid occurs in viscous fluid heaters having a disk-shaped rotor and the like.
When a viscous fluid type heater is operating, heat generated in the heating chamber causes the drive shaft and the rotor to expand. In order to maintain the connection between the rotor and the drive shaft under such circumstances, the rotor is typically made of the same material as the drive shaft (for example, carbon steel, which has heat conductivity of 35 to 60 W/(m.multidot.K)). However, carbon steel is difficult to machine. Also, carbon steel is relatively heavy and thus increases the weight of the heater.